Femt, also known as the King of Depravity, is a major antagonist in the anime Kekkai Sensen. He is a prominent and self-proclaimed member of the Thirteen Kings, a group of powerful and malevolent beings who wield significant influence over the chaotic metropolis of Hellsalem's Lot. His very nature is defined by an insatiable love for chaos, destruction, and the creation of theatrical spectacles of disorder, which he pursues as a form of personal entertainment rather than for any grander ideological purpose.

Personality-wise, Femt is a sadistic, flamboyant, and utterly unpredictable madman who embodies the principle of living solely for pleasure. He holds a deep-seated contempt for anything mundane or ordinary, and his primary drive is to shatter the status quo of the world around him. Despite his hostility towards order, he is not a mindless brute; his chaos is carefully orchestrated. He possesses a highly theatrical flair, often taking over media broadcasts to announce his destructive games or confronting his enemies with a cackling glee that makes him seem like a performer on a stage. His cruelty is refined, as he will meticulously craft scenarios to provoke the citizens of Hellsalem's Lot, believing that a challenge from them is what makes his games genuinely entertaining, as simply obliterating the city would, in his view, be boring. This twisted sense of fair play demonstrates that his motivation is less about conquest and more about the joy of seeing how people react when pushed to their limits.

Within the story, Femt acts as a recurring agent of chaos who frequently clashes with Libra, the secret organization dedicated to preserving the peace of the city. His role is that of a wildcard villain who introduces high-stakes crises for the protagonists to solve. For instance, he has been known to kidnap random civilians and place monstrous creatures on their heads simply to create a public disturbance. He views the world and its inhabitants as pieces on a game board, and he is happiest when he is moving those pieces to cause maximum disruption. His key relationships are primarily adversarial, most notably with Leonardo Watch, the series' protagonist. In a significant encounter, Femt confronts Leo in a metaphysical game of wits, and while he is manipulative and dangerous, he ultimately releases Leo, deciding that watching the outcome of the boy's struggle will be a more entertaining show than simply defeating him. This interaction highlights Femt's primary function in the narrative: not to be a final boss to be defeated, but to be a catalyst for the plot who tests the resolve of the heroes.

Femt is not merely a schemer but also a highly capable genius with a background as a skilled scientist, proficient in both Earthly and otherworldly sciences. This intellect allows him to create a vast array of bizarre monsters and technological mayhem, which he unleashes upon the city for his amusement. In addition to his scientific prowess, he wields considerable supernatural power. He is capable of feats such as manipulating time, warping space, and moving between dimensions, abilities that he uses to infiltrate secure locations and conduct his elaborate games. His appearance is as distinctive as his personality: a tall figure with long blond hair, always dressed in a black outfit topped with an expensive laboratory coat and white gloves. He typically conceals the upper part of his face with an iron mask, adding to his enigmatic and menacing presence. While his personal development is largely static as an agent of chaos, he serves as a crucial element in the development of the world around him, embodying the constant, unpredictable danger that defines life in Hellsalem's Lot.